One of the aims of this study is to develop a field test suitable for the screening of subclinical malabsorption of food nutrients and also capable of detecting alterations in the G.I. ecology of individuals subjected to a poor nutrition and low levels of sanitation as it occurs in rural Guatemala. Furthermore, it is intended to determine the extent to which the diet of these individuals, characterized by its high content of poorly digestible carbohydrates, influences their G.I. ecology and the utilization of nutrients. During the standardization of the test d-Xylose, raffinose, and a bean or corn-bean diet will be fed to rural Guatemalan adult male volunteers hospitalized in a rural metabolic ward or at Clinical Center. H2 contents will be determined chromatographically in breath samples obtained every 30-60 min for a 5-7-hour period. The time sequence of H2 formation may help to detect upper G.I. bacterial overgrowth while the volume of H2 produced will serve to indicate the amount of non-absorbed carbohydrate available for bacterial fermentation. The G.I. microflora of some of these subjects will be characterized and compared with the determinations of H2 obtained. After standardization this test will be used to study rural populations of Guatemala. Nutrient absorption will be evaluated during a 28-day balance study using a highly absorbable formula and a rural Guatemalan diet administered 14-day periods. Determinations of N, fat, Ca, K, and energy content will be carried out in food and biological samples. Different hematological parameters, urinary indican-urobilinogen contents and parasitological workup will be also performed. Studies will be replicated in a small number of healthy North American male adults in the Human Nutrition Laboratory of the University of California at Berkeley. Comparison of the responses should clarify the basis of low urinary excretion of xylose in Guatemalan adults and how the rural Guatemalan diet is handled by individuals living in environments with different levels of sanitation.